Talks and Poster Presentations (without Proceedings-Entry):
C. Knoll, D. Müller, W. Artner, Jan Welch, A. Werner, M. Harasek, P. Weinberger:
"Oxalate-hydrates in thermochemical energy storage - a so far neglected class of salt hydrates";
Talk: The International Symposium on Energy 7,
Aiming for a sustainable energy economy, recycling of waste heat could contribute to an improved energy balance. In this context, thermochemical energy storage (TCES) is considered as promising approach allowing for a decoupling of energy production and consumption. Based on a reversible chemical reaction, heat is stored during the endothermic decomposition reaction. On recombination of the products an exothermic reaction occurs, releasing the previously stored heat. Depending on the temperature level of the waste heat source, different classes of materials are best suited for a TCES-process. For temperatures up to 200 °C salt hydrates, undergoing reversible dehydration / hydration cycles, are the material of choice. Key issues using salt hydrates are slow and incomplete rehydration, as well as solubility of the materials. To overcome such limitations, various oxalate-hydrates M(C2O4)∙xH2O, [M = NH4, K, Mg, Ca, Sr, Ba, Fe, Co] were investigated by means of in-situ powder X-Ray diffraction and thermogravimetry / differential scanning calorimetry. From the selected materials only for M = NH4, K, Mg, Ca fast and complete rehydration behavior was found. In all cases the rehydration rate and completeness was strongly affected by the H2O-partial pressure. The best results were obtained for CaC2O4∙H2O, which shows remarkable cycle stability over more than 100 cycles. Additionally, by variation of the H2O partial pressure during the rehydration reaction the material can be used as chemical heat pump.
oxalate hydrates, cycle stability, water vapour concentration, chemical heat pump, thermochemical energy storage
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